Why negative battery cable grounded to motor?

[DanW]

I was planning on moving the negative battery cable up on the frame to hide it rather than its original placement on the motor. My question is...what was the reason/benefit for being bolted to the engine?

 

[arcticXS]

This is because the largest current on the bike goes to the starter, so this gives the most direct path/least resistance for the starter current. If you have an electric starter, you can still connect the negative battery cable to the frame, if you run another, equally thick cable from the frame to the engine.
Even with no electric starter, you need a "grounding strap" between frame and engine, to ensure properly functioning ignition and charging.

 

[DanW]

Alright--that makes sense. Thanks. I'll have to find a less visable place on the motor to hide it better. Thanks again.